Ireland skipper Brian O'Driscoll has called for his charges to up their game following their 22-10 win over the United States in New Plymouth.

Two tries from Tommy Bowe and a touch down by Rory Best failed to paper over the cracks of a display that will have concerned the Irish management. O'Driscoll delivered an honest assessment of their opening World Cup game and admitted a significant improvement would be needed against Australia next Saturday.

"We didn't play well, we really had to fight for our win and we have got a hell of a lot to work on," said the Ireland captain. "We turned the ball over too much. Our performance was typified by the last play of the game (when America scored an intercept try).

"We have got a big challenge now against Australia. There were aspects that were disappointing, but the most important thing was that we broke our losing sequence and won the game.

"If we're relying on bonus points to get us through the group stages we're going to be in trouble. There were disappointments, but it's not the end of the world.

"There are plenty of things we can work on that we can fix. When you look at individual errors you have to look at your own performance.

"If everyone can tighten that up, then straight away we'll be on a better footing. There were some good aspects to it. We took our tries extremely well. But when it finishes on an intercept try and you don't have a chance to reply, it leaves a bitter taste in the mouth."

Rain and strong wind made conditions at Stadium Taranaki challenging, while the USA side were also motivated by the 10th anniversary of September 11. But Ireland still should have done better against a team positioned 10 places below them in the world rankings at 18th.

The faltering performance has only heightened concerns raised during the four defeats in the warm-up internationals that the team is locked in a downward spiral. But O'Driscoll said: "We start from the USA game only. The four warm-up games were exactly that. This is the World Cup.

"We can't afford slip-ups or to lose too many games in the pool stages. You have to win games ugly if necessary. Today might not have been a thing of beauty but we got across the line and that's the most important thing.

"We're sitting on four points when at the start of the day we had nothing. It's something to work on. Now comes a huge challenge - playing Australia."

Former Ireland boss Eddie O'Sullivan, now coach of the USA, was delighted by the commitment shown by the Eagles.

"We fought our way from the first minute until the last. We were punch drunk at times, but we were very spirited," he said. "The lads put in a huge performance. All it takes is for a couple of lads to bail and then the floodgates open and you've conceded 20 or 30 points.

"There were times when I thought that would happen but the guys just dug deeper and deeper. We could have got a right hiding so the lads deserved a lot of credit for hanging in there."